In signing the National Environmental Policy Act on Jan. 1, 1970, President Nixon declared that America must reclaim the purity of its air and water. In furtherance of our government's objectives of eliminating pollution a Presidential Commission was appointed to study the causes of pollution and to recommend solutions thereto. On Aug. 10, 1970, their initial report was made public. It included as one recommendation for reclaiming our waters that "polyphosphate builders" be eliminated from detergent compositions.
For a number of years now, the polyphosphates and especially sodium tripolyphosphate (STP) and tetrasodium pyrophosphate (TSPP) have been the backbone of detergent compositions. The role of these builders is a complex one but two of their principal, required functions are to sequester calcium and magnesium salts in the wash water and to enhance the cleaning capabilities of detergent compounds.
Millions of tons of the polyphosphates are sold annually in the United States for use as builders. Sometime during the life span of these detergents they are usually discharged into our nation's lakes and streams.
In recent years a growing amount of evidence has indicated that the polyphosphates have deleterious effects on our streams and lakes. For example, it has been observed that the growth of certain algae in bodies of water is stimulated by the polyphosphates, thus causing serious damage to various kinds of aquatic plants and fish. The algae buildup also produces a very unpleasant sight. And, before too long, conventional water sports are no longer possible.
Prior to the Environmental Act of 1970, one of the largest concerted industrial efforts was instituted to discover a satisfactory, nonpolluting replacement for the polyphosphates in detergent compositions. It is still being actively pursued. Recently, one major seller of cleaning products advertised that it had, without success, spent over three million dollars in an effort to discover such a replacement. Despite this concerted effort, no such replacement has been announced by anyone.
Other builder detergent salts are known or have been announced. Some supposedly present no pollution problems. While they are thus superior to the polyphosphates in that respect they are inferior in other ways. For example, some have been too costly to manufacture, others have failed to function properly as builders, to display the required synergistic action in combination with detergent compounds, and still others have become suspect of producing undesirable side effects.
One builder salt which some detergent manufacturers have recently begun commercially using is the trisodium salt of nitrilotriacetic acid. While the use of this salt has reduced the amounts of polyphosphates required in a particular detergent composition, it has not eliminated the polyphosphates entirely. In such compositions polyphosphates are still employed. Moreover, in recent months some opinions have been expressed that this compound may contribute to the growth of, or cause cancer.
Builder salts other than the alkali metal salts of the aminopolycarboxylic acids have been proposed as polyphosphate replacements. For instance, in Diehl U.S. Pat. No. 3,308,067, a polyphosphate substitute is disclosed. The inventor describes his builder salts as being water soluble salts of polymeric aliphatic polycarboxylic acids. He describes the "essential" structural characteristics of such salts as follows:
1. A minimum molecular weight of about 350 calculated as the acid form. PA1 2. An equivalent weight of about 50 to about 80 calculated as the acid form. PA1 3. At least 45 mole percent of the monomeric species comprising the polymer aliphatic polycarboxylic acid species having at least two carboxyl radicals separated from each other by not more than two carbon atoms. PA1 4. And, the site of attachment to the polymer chain of any carboxyl-containing radical being separated by not more than three carbon atoms along the polymer chain from the site of attachment of the next carboxyl-containing radical.
He points out later in the patent that as the molecular weight decreases below 350, the builder properties decrease substantially.
Still other builder salts have been produced as polyphosphate replacements namely, sodium phytate, the water soluble salts of mehtylene diphosphoric acid, etc. A review of such salts and the patents disclosing them is contained in U.S. Pat. 3,346,873.
Despite the millions of dollars which have been spent in an attempt to discover polyphosphate replacements there has been no compound discovered which favorably compares with the polyphosphates on a price and performance basis and which eliminates the pollution problem. To these ends this invention is directed.
One of the major areas in which phosphates are employed as builders in detergent compositions is in the area of mechanical dishwashing. Millions of pounds of phosphated dishwashing detergent compositions are sold each year for home, restaurant and institutional use. Such compositions customarily contain at least 25% by weight of sodium tripolyphosphate, chlorinated trisodium phosphate and/or tetrasodium pyrophosphate.
The development of mechanical dishwashing detergents began only in recent years. Until the discovery that phosphates could be used as "builders" in dishwashing detergents (U.S. Pat. No. 2,374,100) mechanical dishwashers were not in widespread use. Prior to that time other types of builder salts as for example sodium carbonate, sodium bicarbonate, sodium orthophosphate, and the sodium silicates were available but could not be used in combination with other materials to provide a satisfactory dishwashing composition.
With the introduction of the phosphates into dishwashing detergents in the mid 1930's mechanical dishwashing increased. However, one problem that was encountered and which remained unsolved for more than ten years was of water spotting on glassware and other glass items conventionally washed in the dishwasher. Water spots could only be removed by a hand toweling operation after the washing cycle had been completed. The phenomena of water spotting is very complicated and has been studied at length. One study indicates that water spotting is due to three factors, fat and protein soils, detergent builders, and water hardness.
The role that a "builder salt" plays in a mechanical dishwashing composition is much different from the role it plays in the laundering of clothes in a mechanical washing machine. It is recognized that in a clothes washing bath the surfactant, frequently called the detergent, is the material which is responsible for the cleaning of the laundry. In the washing of dishes however the builder itself exerts a true detersive effect and is the principal "detergent" in the system. For this reason it is recognized that materials which function as builders in clothes washing compositions are not necessarily useful in mechanical dishwashing detergents. This recognition is supported by the history of mechanical dishwashing referred to above wherein it is pointed out that although many builders, useful in clothes washing, were available before sodium tripolyphosphate, none were effective.
In 1956 U.S. Pat. No. 2,756,214 issued and disclosed a mechanical dishwashing composition which substantially reduced water spotting. The composition disclosed therein is a binary mixture of a phosphate builder and chlorinated trisodium phosphate. The patent details the water spotting problems which had been long experienced in the industry.
After the issuance of U.S. Pat. No. 2,756,214 other patents were soon granted directed to the use of other chlorine materials for the purpose of eliminating the water spotting problem and it is generally accepted in the art that in order to prevent water spotting a chlorine material is required.
It is also recognized at this time that unless the composition includes a phosphate builder satisfactory performance cannot be obtained. Recent legislation directed to the elimination of phosphates or the lowering of their levels in commercial products have specifically exempted dishwashing from the ban or the reduction in content because the soap and detergent industry has convinced them that there is no satisfactory substitute for such materials.
Besides a phosphate builder and a chlorine material, most dishwashing detergent compositions include a surfactant. The art recognizes that the most desirable one is a nonionic surfactant. One reason why they are more desirable than other types is that they produce low levels of foam in use. Of course, high levels of foam cannot be tolerated in a dishwasher. Unfortunately, however, nonionic surfactants have had to be carefully selected because many are incompatible with the chlorine materials which are customarily employed in the detergent composition. For this reason, many of the desirable nonionic surfactants cannot be employed.
Overlooking the eutrophication problem for a moment, there is one area in which there exists a need to improve the performance of dishwashing detergent compositions. One recognized problem in the use of the phosphates in dishwashing detergents is that the phosphate has a solubility which is less than the other materials which are customarily employed. For this reason the water to the dishwasher must be as hot as possible so that a satisfactory solution is obtained. It can be appreciated that in many instances such a source of hot water is temporarily unavailable in which event the conventional phosphate dishwashing composition will not be dissolved. It has, therefore, been necessary with the prior art products to maintain the temperature of the water in the dishwasher at between about 140.degree. F. and about 190.degree. F. It will be appreciated also that this required water heating increases the cost of each dishwashing cycle over what it would cost if relatively cool water could be used.
The need for a relatively soluble builder-detergent for dishwashing use arises also through the use of mechanical dispensing equipment frequently employed in restaurants and institutional uses. In use, water is conveyed into the dispenser and mixed with a desired quantity of dishwashing detergent. The water-detergent composition solution is then conveyed to the mechanical dishwasher. In order to be useful in such a system the dishwashing detergent composition must first be soluble in water and secondly the various components in the composition must have approximately the same solubility rates. If such was not the case the solution passing to the dishwasher would contain the individual components in an undesired ratio.
In addition to the foregoing requirements which must be met if a dishwashing composition is to be successful there should also be added the requirement that the material be noncaking. This has been one of the reasons why some materials have not been useful as a complete phosphate replacement in mechanical dishwashing compositions.
Even though a detergent composition meets its intended performance criteria and solves the pollution problem, there is still an important criterion that it should satisfy, namely toxicity. The builders of the present invention when formulated in compositions made in accordance with the following instructions have been determined to be nontoxic as that term is employed in the Federal Hazardous Substances Act.
In view of the foregoing, the following have been important objectives of this invention.
1. To produce phosphate free detergent compositions suitable for many uses including laundry or dishwashing detergents;
2. To produce such a detergent composition which is readily soluble in even cold water;
3. To produce such a detergent composition which includes only a minor number of ingredients and whose manufacture is relatively simple;
4. To produce such a detergent composition which does not need a chlorine material to reduce or to eliminate water spotting;
5. To produce such a detergent composition which is satisfactory for home and commercial, i.e., restaurant, etc., use which may be employed in conventional, automatic dispensing equipment; and
6. To produce such a detergent composition which is nontoxic.